JEE MAIN - Physics (2021 - 26th February Evening Shift - No. 20)

1 mole of rigid diatomic gas performs a work of $${Q \over 5}$$ when heat Q is supplied to it. The molar heat capacity of the gas during this transformation is $${xR \over 8}$$. The value of x is _________. [R = universal gas constant]
Answer
25

Explanation

From thermodynamics law:

$$Q = \Delta U + W$$

$$Q = \Delta U + {Q \over 5}$$

$$\Delta U = {{4Q} \over 5}$$

$$n{C_v}\Delta T = {4 \over 5}nC\Delta T$$

$${5 \over 4}{C_v} = C$$

$$C = {5 \over 4}\left( {{f \over 2}} \right)R = {5 \over 4}\left( {{5 \over 2}} \right)R$$

$$C = {{25} \over 8}R$$

$$X = 25$$

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